Monkeys living in forests near Fukushima have levels of radioactive caesium in their muscles that may be dangerous. The monkeys were also found to have lower counts of both red and white blood cells than monkeys living farther north, which may indicate health effects to come.
In Scientific Reports a team led by Kazuhiko Ochiai of the Nippon Veterinary and Life Science University compare 61 Japanese macaques (Macaca fuscata) from near Fukushima with 31 from 400km away. They found a huge range of the radioactivity in the Fukushima monkeys, from 78-1778 Bequerals per kilogram, while their more distant relatives had undetectably low levels.
The irradiated monkeys were living 70km from the Fukushima Daiichi power plant, where three nuclear reactors melted down in March 2011. Humans living in Fukushima itself, much closer to the plant, have shown no such effects, but they are eating a diet sourced from a variety of locations. The monkeys live on fruits, mushrooms and insects. Unsurprisingly, none of these are imported.
The main problematic radioactive isotopes released in nuclear accidents are Iodine 131 and Caesium 137. Unless treated with non-radioactive iodine, the 131I builds up in the thyroid, causing cancer. However, much less is known about the effects of radioactive caesium. The beta and gamma radiation it releases could damage DNA, but since it doesn’t concentrate in any one part of the body, it is hard to measure how much damage is done. The doses detected in the monkeys are far short of those that would cause radiation sickness, and any influence on cancer rates can be hard to pick out from other factors.
The affected monkeys also had decreased counts of both red and white blood cells, consistent with results in people living near Chernobyl. Immature monkeys appeared to have been more affected than adults. No signs of ill health were observed, but healthy white blood cells are essential to protect against infections.
There have been no previous studies on the Fukushima monkeys, so it is possible that some pre-existing condition is causing the low blood cell counts, a claim made by some scientists not involved with the study. However, regional variations have not been observed in Japanese macaques previously.
Previous studies have found radiation from Fukushima has caused abnormalities in butterflies, and reduced the presence of invertebrate species, and the birds that feed on them, but this is the first sign of effects on mammals, let alone a species so close to us.